Semiconductor device

Abstract

To provide a semiconductor device in which leakage current can be reduced.SOLUTION: A semiconductor device comprises: a first conductivity type first semiconductor layer that is provided on a first electrode, and has a plurality of mesa parts which are positioned being apart from each other in a first direction, and which extend in a second direction; a second electrode that is positioned at a recessed part provided on an upper part of the mesa part and extends in a second direction; a gate electrode that is adjacent to the mesa part in the first direction; an insulation film that is provided between the mesa part and the gate electrode; and a second conductivity type second semiconductor layer that contacts with an edge in the second direction of the second electrode. The mesa part has a first side surface that faces the gate electrode through the insulation film in the first direction, and a second side surface that is positioned at the opposite side of the first side surface in the first direction, and with which the second electrode contacts.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The embodiments relate to a semiconductor device. [Background technology]

[0002] A Schottky MOSFET has been proposed as a vertical MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) that achieves an off state by using a depletion layer extending from the Schottky junction between the source electrode and the semiconductor layer at the trench contact area, without providing a p-type base layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-4501 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments provide a semiconductor device capable of reducing leakage current. [Means for solving the problem]

[0005] According to an embodiment, a semiconductor device includes: a first electrode; a first semiconductor layer of a first conductivity type provided on the first electrode, the first semiconductor layer having a plurality of mesa portions spaced apart in a first direction and extending in a second direction perpendicular to the first direction; a second electrode located in a recess provided in an upper portion of the mesa portion and extending in the second direction; a gate electrode adjacent to the mesa portion in the first direction; an insulating film provided between the mesa portion and the gate electrode; and a second semiconductor layer of a second conductivity type in contact with an end of the second electrode in the second direction. The mesa portion has a first side surface facing the gate electrode in the first direction via the insulating film, and a second side surface located opposite the first side surface in the first direction and in contact with the second electrode. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a schematic plan view of a semiconductor device according to an embodiment; [Figure 2] FIG. 2 is an enlarged schematic plan view of part A in FIG. [Figure 3] 3 is a cross-sectional view taken along the line AA in FIG. 2. [Figure 4] 3 is a cross-sectional view of FIG. 2 taken along line B-B. [Figure 5] 3 is a cross-sectional view taken along CC in FIG. 2. [Figure 6] 3 is a cross-sectional view taken along the line DD in FIG. 2. [Figure 7] FIG. 10 is a schematic plan view of a semiconductor device according to a second embodiment. [Figure 8] 8 is a cross-sectional view taken along the line E-E in FIG. 7. [Figure 9] FIG. 10 is a schematic plan view of a semiconductor device according to a first modified example of the second embodiment. [Figure 10] FIG. 10 is a schematic plan view of a semiconductor device according to a second modification of the second embodiment. [Figure 11] FIG. 10 is a schematic plan view of a semiconductor device according to a third modified example of the second embodiment. [Figure 12] FIG. 10 is a schematic plan view of a semiconductor device according to a third embodiment. [Figure 13] 13 is a cross-sectional view of FIG. 12 taken along line F-F. DETAILED DESCRIPTION OF THE INVENTION

[0007] Each embodiment will be described below with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals. In the drawings shown below, directions are indicated by the X-axis, Y-axis, and Z-axis. The direction along the X-axis is the first direction X. The direction along the Y-axis is the second direction Y, which is perpendicular to the first direction X. The direction along the Z-axis is the third direction Z, which is perpendicular to the first direction X and the second direction Y. In this specification, the width in a certain direction refers to the maximum width in that certain direction.

[0008] As shown in FIG. 1, the semiconductor device of each embodiment has an element region 101 and a termination region 102. The termination region 102 continuously surrounds the element region 101. The semiconductor device includes a semiconductor layer. In this specification, the first conductivity type of the semiconductor layer is defined as n-type, and the second conductivity type is defined as p-type. The first conductivity type may be p-type, and the second conductivity type may be n-type. The semiconductor layer is, for example, a silicon layer. Alternatively, the semiconductor layer may be a silicon carbide layer, a gallium nitride layer, or the like.

[0009] A second electrode 92 and a gate pad 93 are provided on the semiconductor layer. The gate pad 93 is electrically connected to a gate electrode, which will be described later. For example, a wire is bonded to each of the second electrode 92 and the gate pad 93, and the second electrode 92 and the gate electrode are electrically connected to an external circuit.

[0010] [First embodiment] The semiconductor device of the first embodiment will be described with reference to FIGS.

[0011] Fig. 2 is an enlarged schematic plan view of part A in Fig. 1. Note that Fig. 7 and Figs. 9 to 12, which will be described later, are also enlarged schematic plan views of part A in Fig. 1.

[0012] FIG. 3 is a cross-sectional view taken along line AA in FIG. FIG. 4 is a cross-sectional view taken along the line BB in FIG. FIG. 5 is a cross-sectional view taken along line CC in FIG. FIG. 6 is a cross-sectional view taken along line DD in FIG.

[0013] As shown in FIG. 3 , the semiconductor device of the embodiment includes a first electrode 91, an n-type first semiconductor layer 10 provided on the first electrode 91, and a second electrode 92 provided on the first semiconductor layer 10. The semiconductor device of the embodiment has, for example, a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) structure. The first electrode 91 is a drain electrode of the MOSFET, and the second electrode 92 is a source electrode of the MOSFET. For example, a positive potential is applied to the first electrode 91, and 0 V is applied to the second electrode 92. In an on-state in which the gate voltage of the gate electrode 40 is made higher than the threshold voltage, a current flows vertically (in a third direction Z) between the first electrode 91 and the second electrode 92 through the first semiconductor layer 10. In the third direction Z, the direction from the first electrode 91 to the second electrode 92 is defined as up or upward, and the direction from the second electrode 92 to the first electrode 91 is defined as down or downward.

[0014] The first semiconductor layer 10 has a plurality of mesa portions 11 that are spaced apart from each other in a first direction X and extend in a second direction Y. A trench structure having a gate electrode 40 is provided adjacent to the mesa portion 11 in the first direction X. The plurality of trench structures are aligned in the first direction X. Each trench structure extends in the second direction Y. The mesa portion 11 and the trench structure are arranged in an element region 101.

[0015] The second electrode 92 is located in a recess 11A provided in the upper part of the mesa portion 11. The recess 11A and the second electrode 92 in the recess 11A extend in the second direction Y. The second electrode 92 is also provided on the trench structure portion.

[0016] The trench structure further includes an insulating layer 52 provided between the gate electrode 40 and the second electrode 92 in the third direction Z, and a first insulating film 51 provided between the mesa portion 11 and the gate electrode 40 in the first direction X.

[0017] The trench structure may further include a field plate electrode 60 and a second insulating film 53. The field plate electrode 60 is located below the gate electrode 40. The second insulating film 53 is provided between the gate electrode 40 and the field plate electrode 60, and between the field plate electrode 60 and the first semiconductor layer 10.

[0018] A portion of the mesa portion 11 located between the trench structure and the second electrode 92 (recess 11A) has a first side surface 11S1 and a second side surface 11S2. The first side surface 11S1 faces the gate electrode 40 in the first direction X with the first insulating film 51 interposed therebetween. The second side surface 11S2 is located on the opposite side of the first side surface 11S1 in the first direction X. The second electrode 92 in the recess 11A contacts the second side surface 11S2.

[0019] The portion of the mesa portion 11 between the first side surface 11S1 and the second side surface 11S2 has a channel portion 11B and a contact portion 11C. The channel portion 11B faces the gate electrode 40 in the first direction X via the first insulating film 51. The contact portion 11C is provided on the channel portion 11B. The n-type impurity concentration of the contact portion 11C is higher than the n-type impurity concentration of the channel portion 11B. The mesa portion 11 in the element region 101 does not include a p-type semiconductor layer.

[0020] The second electrode 92 is made of a metal material. The second electrode 92 and the second side surface 11S2 of the channel portion 11B form a Schottky junction. The second electrode 92 is in direct contact with the second side surface 11S2 of the channel portion 11B. Alternatively, the second electrode 92 may be in contact with the second side surface 11S2 of the channel portion 11B via an insulating film. The second electrode 92 is in ohmic contact with the second side surface 11S2 of the contact portion 11C.

[0021] The semiconductor device further includes an n-type third semiconductor layer 30 provided between the first electrode 91 and the first semiconductor layer 10 and electrically connected to the first electrode 91. The n-type impurity concentration of the third semiconductor layer 30 is higher than the n-type impurity concentration of the first semiconductor layer 10.

[0022] In an on-state in which the gate voltage of the gate electrode 40 is set higher than the threshold voltage, a current flows between the first electrode 91 and the second electrode 92 via the contact portion 11C and the channel portion 11B.

[0023] When the gate voltage of the gate electrode 40 is lower than the threshold voltage, for example, 0 V, the channel portion 11B is depleted by a depletion layer extending in the first direction X from the Schottky junction between the second side surface 11S2 of the channel portion 11B and the second electrode 92, and a depletion layer extending in the first direction X from the boundary between the second side surface 11S2 of the channel portion 11B and the first insulating film 51 of the trench structure portion, and the semiconductor device is turned off.

[0024] To facilitate depletion of the channel portion 11B, it is preferable that the width of the channel portion 11B in the first direction X be small. For example, the width of the channel portion 11B in the first direction X is smaller than the width of the second electrode 92 in the first direction X within the recess 11A. The threshold voltage of the semiconductor device depends on the width of the channel portion 11B in the first direction X. Furthermore, the withstand voltage and threshold voltage of the semiconductor device depend on the barrier height between the metal of the second electrode 92 and the first semiconductor layer 10. For example, by using a metal with a high work function, such as Pt, for the second electrode 92, the barrier height between the second electrode 92 and the first semiconductor layer 10 can be increased, thereby increasing the withstand voltage.

[0025] The semiconductor device according to the embodiment can be used as a switching element in applications such as inverters and motor drives. In this case, the semiconductor device is required to function as a freewheeling diode that passes a reverse current generated during switching. In this case, the second electrode 92 preferably contacts the first semiconductor layer 10 at the bottom of the recess 11A. This ensures a current path (a current path that does not pass through the channel portion) when the semiconductor device operates as a freewheeling diode.

[0026] The first semiconductor layer 10 is also provided in a termination region 102 of the semiconductor device. No contact portion 11C is provided in the termination region 102. Furthermore, a p-type second semiconductor layer 20, which will be described later, is provided in the termination region 102.

[0027] A side surface of the second electrode 92 in the first direction X faces the trench structure portion. In contrast, as shown in FIG. 2 , an end surface 92A of the second electrode 92 in the second direction Y does not face the trench structure portion in the second direction Y. Therefore, in a region adjacent to the end surface 92A of the second electrode 92, a depletion layer cannot extend in the second direction Y from the boundary between the trench structure portion and the first semiconductor layer 10. This can cause a leakage current to flow along the end surface 92A of the second electrode 92.

[0028] 2 and 4, a p-type second semiconductor layer 20 is provided in contact with an end portion of the second electrode 92 in the second direction Y. The second semiconductor layer 20 is provided in the first semiconductor layer 10, and is in contact with an end surface 92A and a bottom surface 92B of the end portion of the second electrode 92 in the second direction Y. The pn junction between the second semiconductor layer 20 and the first semiconductor layer 10 can reduce leakage current in a region adjacent to the end surface 92A of the second electrode 92.

[0029] 2 and 5, in the termination region 102, the gate electrode 40 is electrically connected to a gate wiring (not shown) provided on the insulating layer 52 via a first connection portion 71 that penetrates the insulating layer 52. The gate wiring is electrically connected to the gate pad 93 shown in FIG.

[0030] As shown in Figures 2 and 6, in the termination region 102, the field plate electrode 60 is electrically connected to a second electrode 92 provided on the insulating layer 52 via a second connection portion 72 that penetrates the insulating layer 52.

[0031] [Second embodiment] The semiconductor device of the second embodiment will be described with reference to Figures 7 to 11. In the semiconductor device of the second embodiment, the same components as those in the semiconductor device of the first embodiment are denoted by the same reference numerals, and the description will focus mainly on components that differ from those in the semiconductor device of the first embodiment.

[0032] As shown in FIGS. 7 and 8, the semiconductor device of the second embodiment includes, in the termination region 102, a first conductive member 81 that extends in the first direction X and faces an end face 92A of the second electrode 92 in the second direction Y.

[0033] In the termination region 102, a trench structure similar to that in the element region 101 is arranged to extend in the first direction X. For example, the trench structure of the element region 101 and the trench structure of the termination region 102 are formed simultaneously. For example, the first conductive member 81 in the trench structure of the termination region 102 is formed simultaneously and from the same material as the gate electrode 40 in the trench structure of the element region 101. Like the trench structure of the element region 101, the trench structure of the termination region 102 has a first insulating film 51, a second insulating film 53, a field plate electrode 60, and an insulating layer 52.

[0034] 8, a portion 11D of the first semiconductor layer 10 is provided between an end surface 92A of the second electrode 92 and the first conductive member 81 in the second direction Y. A Schottky junction is formed between the end surface 92A of the second electrode 92 and the portion 11D of the first semiconductor layer 10. The first insulating film 51 is provided between the portion 11D of the first semiconductor layer 10 and the first conductive member 81 in the second direction Y.

[0035] According to the second embodiment, the portion 11D of the first semiconductor layer 10 can be depleted by a depletion layer extending in the second direction Y from the Schottky junction between the end face 92A of the second electrode 92 and the portion 11D of the first semiconductor layer 10, and a depletion layer extending in the second direction Y from the boundary between the portion 11D of the first semiconductor layer 10 and the first insulating film 51. This reduces leakage current in a region adjacent to the end face 92A of the second electrode 92. To make it easier to deplete the portion 11D of the first semiconductor layer 10, the width in the second direction Y of the portion 11D of the first semiconductor layer 10 is preferably smaller than the width in the second direction Y of the first conductive member 81.

[0036] For example, the trench formed in the element region 101 and the trench formed in the termination region 102 are connected to each other, and the first conductive member 81 is connected to the gate electrode 40 in these trenches.

[0037] 7, the semiconductor device further includes, in the termination region 102, a second conductive member 82 connected to the first conductive member 81 and extending in the second direction Y. The gate electrode 40 and the second conductive member 82 extend in opposite directions from the first conductive member 81. The gate electrode 40 extends from the first conductive member 81 toward the element region 101, and the second conductive member 82 extends from the first conductive member 81 toward the termination of the semiconductor device.

[0038] For example, a trench structure including a gate electrode 40, a trench structure including a first conductive member 81, and a trench structure including a second conductive member 82 are formed in the same process. The gate electrode 40, the first conductive member 81, and the second conductive member 82 are formed simultaneously using the same material. The trench structure including the second conductive member 82 has a first insulating film 51, a second insulating film 53, a field plate electrode 60, and an insulating layer 52, similar to the trench structure in the element region 101.

[0039] 5, the end of the second conductive member 82 in the second direction Y can be connected to the gate wiring and the gate pad 93 via the first connection portion 71. Therefore, the gate electrode 40 is electrically connected to the gate wiring and the gate pad 93 via the first conductive member 81 and the second conductive member 82.

[0040] 6, the field plate electrode 60 is continuous below the gate electrode 40, below the first conductive member 81, and below the second conductive member 82. The end of the field plate electrode 60 in the second direction Y located below the second conductive member 82 is connected to the second electrode 92 via the second connection portion 72.

[0041] 7, the gate electrode 40 extending in the second direction Y and the second conductive members 82 extending in the second direction Y are offset from each other in the first direction X. Alternatively, as shown in FIG. 10, the trench structure extending in the first direction X and the trench structure extending in the second direction Y may cross each other. Compared to the trench layout of FIG. 10, the trench layout of FIG. 7 can improve the embeddability when embedding the conductive material that will become the gate electrode 40, the first conductive members 81, and the second conductive members 82 into trenches that are formed collectively.

[0042] 9, the second conductive member 82 may be omitted. A trench structure including the gate electrode 40 and extending in the second direction Y and a trench structure including the first conductive member 81 and extending in the first direction X are connected in a T-shape.

[0043] As shown in FIG. 11, the trench structure including the gate electrode 40 and extending in the second direction Y and the trench structure including the first conductive member 81 and extending in the first direction X do not have to be connected.

[0044] [Third embodiment] A semiconductor device of the third embodiment will be described with reference to Figures 12 and 13. The semiconductor device of the third embodiment has a configuration in which the p-type second semiconductor layer 20 of the first embodiment is combined with a trench structure including the first conductive member 81 of the second embodiment.

[0045] In the termination region 102, the second semiconductor layer 20 is located between the end face 92A of the second electrode 92 and the first conductive member 81 in the second direction Y. The second semiconductor layer 20 contacts the end face 92A and the bottom face 92B of the second electrode 92 at the end in the second direction Y.

[0046] The second semiconductor layer 20 is provided in the second direction Y between the end face 92A of the second electrode 92 and the first conductive member 81. A first insulating film 51 is provided between the second semiconductor layer 20 and the first conductive member 81 in the second direction Y.

[0047] According to the third embodiment, the second semiconductor layer 20 adjacent to the end face 92A of the second electrode 92 can be depleted by a depletion layer extending in the second direction Y from the boundary between the second semiconductor layer 20 and the first insulating film 51. In addition, the pn junction between the second semiconductor layer 20 and the first semiconductor layer 10 can reduce leakage current in the region adjacent to the end face 92A of the second electrode 92.

[0048] In the first and third embodiments, depending on the work function of the metal of the second electrode 92 and the impurity concentration of the second semiconductor layer 20, a Schottky junction can be formed between the end face 92A of the second electrode 92 and the second semiconductor layer 20. In this case, a depletion layer can extend from the interface between the end face 92A of the second electrode 92 and the second semiconductor layer 20.

[0049] The film thickness of the first insulating film 51 in the termination region 102 may be set to be thicker than the film thickness of the first insulating film 51 in the element region 101. This can improve the breakdown voltage.

[0050] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0051] 10...first semiconductor layer, 11...mesa portion, 11A...recess, 11B...channel portion, 11C...contact portion, 11S1...first side surface, 11S2...second side surface, 20...second semiconductor layer, 30...third semiconductor layer, 40...gate electrode, 51...first insulating film, 52...insulating layer, 53...second insulating film, 60...field plate electrode, 71...first connecting portion, 72...second connecting portion, 81...first conductive member, 82...second conductive member, 91...first electrode, 92...second electrode, 92A...end surface, 93...gate pad, 101...element region, 102...termination region

Claims

1. A first electrode; a first semiconductor layer of a first conductivity type provided on the first electrode, the first semiconductor layer having a plurality of mesa portions spaced apart from each other in a first direction and extending in a second direction perpendicular to the first direction; a second electrode located in a recess provided in an upper portion of the mesa portion and extending in the second direction; a gate electrode adjacent to the mesa portion in the first direction; an insulating film provided between the mesa portion and the gate electrode; a second semiconductor layer of a second conductivity type in contact with an end portion of the second electrode in the second direction; Equipped with The mesa portion is a first side surface facing the gate electrode in the first direction with the insulating film interposed therebetween; a second side surface located opposite to the first side surface in the first direction and in contact with the second electrode; A semiconductor device having:

2. A first electrode; a first semiconductor layer of a first conductivity type provided on the first electrode, the first semiconductor layer having a plurality of mesa portions spaced apart from each other in a first direction and extending in a second direction perpendicular to the first direction; a second electrode located in a recess provided in an upper portion of the mesa portion and extending in the second direction; a gate electrode adjacent to the mesa portion in the first direction; an insulating film provided between the mesa portion and the gate electrode; a first conductive member extending in the first direction and facing an end of the second electrode in the second direction; Equipped with The mesa portion is a first side surface facing the gate electrode in the first direction with the insulating film interposed therebetween; a second side surface located opposite to the first side surface in the first direction and in contact with the second electrode; A semiconductor device having:

3. 3. The semiconductor device according to claim 2, further comprising a second semiconductor layer of a second conductivity type located between the end of the second electrode and the first conductive member in the second direction and in contact with the end of the second electrode.

4. 4. The semiconductor device according to claim 2, wherein the first conductive member is connected to the gate electrode.

5. a second conductive member connected to the first conductive member and extending in the second direction; The semiconductor device according to claim 4 , wherein the gate electrode and the second conductive member extend in opposite directions from the first conductive member.

6. The semiconductor device according to claim 5 , wherein the gate electrode and the second conductive member are offset from each other in the first direction.

7. The mesa portion is a channel portion located between the gate electrode and the second electrode in the first direction; a contact portion provided on the channel portion and having a first conductivity type impurity concentration higher than that of the channel portion; 3. The semiconductor device according to claim 1, further comprising:

8. the channel portion and the second electrode form a Schottky junction; The semiconductor device according to claim 7 , wherein the second electrode is in ohmic contact with the contact portion.

Images